Tectus niloticus (Tegulidae, Gastropod) as a novel vector ...
Mollusks-“soft bodied”Class Gastropoda •The shell of a gastropod is always one piece...
Transcript of Mollusks-“soft bodied”Class Gastropoda •The shell of a gastropod is always one piece...
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Mollusks- “softbodied”
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Objectives
• Understandthetaxonomicrelationshipsandmajorfeaturesofmollusks
• Learntheexternalandinternalanatomyoftheclamandsquid
• Understandthemajoradvantagesandlimitationsoftheexoskeletonsofmollusksinrelationtothehydrostaticskeletonsofwormsandtheendoskeletonsofvertebrates,whichyouwillexaminelaterinthesemester
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Section21.5 Figure21.15
Keyfeatures
MollusksAreSoftandUnsegmented
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Section21.5 Figure21.15
Diversity
MollusksAreSoftandUnsegmented
Chiton: ©Kjell B. Sandved/Science Source; bivalve: ©Andrew J. Martinez/Science Source; snail: ©Digital Vision RF; slug: ©Steven P. Lynch/The Mcgraw-Hill Companies; octopus: ©Fred Bavendam/Minden Pictures; squid: ©Comstock Images/PictureQuest RF
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Phylum Mollusca
•Includes snails and slugs, oysters and clams, and octopuses and squids.
Bivalves Nautilus
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Characteristics
•Bi-lateral&Triploblastic•Unsegmentedasapposedtonearestrelative
•Dioecious•Softbodiedcoveredbycalcareous shellthatmayormaynotformahard,calciumcarbonateshell
•Secondlargestanimalphylum
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• Complete,one-waydigestivetractwithamouth&anus
•Haveafully-linedcoelom,buttypicallylimitedtoaroundheart
• Cephalization - haveadistinctheadwithsenseorgans&brain
•Digestivesystemiscomplex&hasascraping,mouth-likestructurecalledtheradula
•Opencirculatorysystem(exceptforcephalopods)
•Gothroughfree-swimminglarvalstagecalledtrochophore
• Chromatophores- camouflagingpigmentsinsquid&octopi
Characteristics
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•Mostmollusksaremarine•Somegastropodsandbivalvesinhabitfreshwater
•Afewgastropods(slugs&snails)areterrestrial.
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MolluskGeneralBodyPlan
Allmolluskshaveasimilarbodyplan:
1. Muscularfoot:a) Broad,flat,muscularorganforlocomotionb) Specializedpartofventralbodywallc) Snailsuseforcreepingoversurfacesd) Clamsuseforplowinginmde) Squidsuseforcatchingprey
2. Mantle(AKAShell):a) hardstructurecaninternalorexternalb) Specializedpartofdorsalbodywallc) Mantlecontainsglandsthatmakeshell(inmostd) Generallyoverhangsvisceralmass&forms
mantlecavitywhichoftencontaingills
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Allmolluskshaveasimilarbodyplan:
3.Visceralmass:a) Containsallinternalorgans(e.g.digestive,pair
ofkidneys,circulatory,respiratoryandreproductiveorgans).
b) Locatedabovefoot
4.Radula- uniquetomollusk inthatitisaraspingorganw/fileliketeethtoscrape/crushfood5. Gills- toextractoxygenfromwaterandfilterfood
MolluskGeneralBodyPlan
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Head-FootRegion•Mostmolluskshavewelldevelopedheadendswithsensorystructuresthatmaybesimplelightdetectorsorcomplexeyes(cephalopods).
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Shells• Found in snails, bivalve mollusks, chitons, and nautilus• Made of calcium carbonate (limestone) secreted by the mantle
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MantleCavity•Thespacebetweenthemantleandthe visceralmass(bodyorgans)iscalledthemantlecavity.
•Therespiratoryorgans(gillsorlungs)aregenerallyhousedhere.
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Feeding
•The radula is a rasping, tongue like feeding structure found in most mollusks except bivalves.
•Has tiny rows of teeth for scraping.
• Filter feeders usegills to sift food
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Respiration•Aquaticspeciesusegills (foundwithinthemantlecavitytoextractoxygenfromwater
• Landmollusksbreathviaanadaptedmantlecavitylinedwithbloodvessels andmustbekeptmoistforoxygentoenter(i.e.slimysnails)
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Respiration
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CirculatorySystem
•Slowmovingspecieshaveopencirculatorysystem• Bloodnotalwayswithinbloodvessel• Worksthroughbodytissuesinopenspacescalledsinuses
•Fastermovingspecieshaveclosedcirculatorysystem
• Bloodalwayswithinvessels#likeaboss
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ExcretorySystem
•Completedigestivesystem•Solidwasteexpelledthroughanus•Metabolicwaste(ammonia)excretedbynephridia(simplekidney-likeorgan)
•Nephridia removewates andexcretetooutsidethroughskin
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Nephridia- EarlyKidneys
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NervousSystem
•Variesgreatlybetweenspecies•Bi-valveshaveextremelysimplesystemsconsistingofcouplegangliaandnervechords(similartoplanarians)
•Octopi,squid,snailshavedevelopedbrainswithmemoryandlearningcapacity
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BrainDevelopment
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Reproduction•Most mollusks have separate sexes with gonads located in the visceral mass.
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Mollusk Life Cycle
•Most mollusks are dioecious (separate sexes)
•Some are hermaphroditic
•The life cycle of many mollusks includes a free swimming, ciliated larval stage called a TROCHOPHORE
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Major Mollusk Classes
•Four major classes of mollusks:•Class Polyplacophora –the chitons
•Class Gastropoda –snails & slugs
•Class Bivalvia – clams, mussels, oysters
•Class Cephalopoda –octopus & squid
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Class Polyplacophora
•Includes the chitons•Eight overlapping plates
•Can roll up•Live mostly in the rocky intertidal zones.
•Use radula to scrape algae off rocks.
•Water flows over gillsto respire
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Class Gastropoda•Gastro = stomach Podos= foot
•Gastropoda is the largest of the mollusk classes.
•70,000 named species.•Include snails, slugs, sea hares, sea slugs, sea butterflies.
•Marine, freshwater, terrestrial.
•Slugs lack a shell!
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Class Gastropoda
•The shell of a gastropod is always one piece – univalve –and may be coiled or uncoiled.
•The apex contains the oldest and smallest whorl.
•Shells may coil to the right or left – this is genetically controlled.
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Class Gastropoda
The foot has a hard plate (operculum) on it that protects the body when it withdraws into the shell.
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Gastropod Feeding Habits
•Most gastropods are herbivores and feed by scraping off algae using the radula.
•Some are scavengersof dead organisms
•Others are carnivores that drill into other mollusks
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Class Bivalvia
•Bivalve mollusks have two shells (valves).
•Mussels, clams, oysters, scallops, shipworms.
•Mostly sessile filter feeders.
•No head or radula.
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Class Bivalvia•Laterally (right-left) compressed shell•Shells are held together by a hinge ligament•Umbo is the oldest part of the shell•Growth occurs in concentric rings around it.
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Class Bivalvia
•Incurrent and excurrent siphons are used to pump water through the organism for:
1. Gas exchange2. Filter feeding3. Jet propulsion.
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Class Bivalvia - Locomotion
•Bivalves move around by extending the muscular foot between the shells.
•Scallops and file shells swim by clapping their shells together to create jet propulsion.
http://www.youtube.com/watch?v=vmi_I8QW5eo
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Class Bivalvia
•Like other mollusks, bivalves have a coelom and an open circulatory system.
•They breathe through gills and filter feed
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Class Bivalvia•Scallops have a row of small blue eyes along the mantle edge. Each eye has a cornea, lens, retina, and pigmented layer.
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Class Cephalopoda• Kaphale = head Podos = foot• Cephalopods include octopuses, squid, nautiluses and cuttlefish.
• Marine carnivores with beak-like jaws Surrounded by tentacles modified from their foot.
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Class Cephalopoda - Shells
•Shells of the Nautilus are made buoyant by a series of gas chambers.
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Class Cephalopoda - Shells
•Cuttlefish have a small curved shell, completely enclosed by the mantle and are masters of camouflage.
Didyouseethat?
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Class Cephalopoda - Shells
•In squid, the shell has been reduced to a small strip called the pen, which is enclosed in the mantle.
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Class Cephalopoda - Locomotion
•Cephalopods swim by expelling water from the mantle cavity through a ventral funnel.
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Class Cephalopoda
•Most cephalopods have complex eyes with cornea, lens, chambers, and retina.
•Largest invertebrate brain
•Closed circulation
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Protection•Color changes effected by chromatophores(pigment cells)
•Allows them to blend into their background•Squirting out water by jet propulsion helps escape predators
•Squids also release an inky substance into the water
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Class Cephalopoda - Reproduction
• Sexes are separate in cephalopods.
• Juveniles hatch directly from eggs –no free-swimming larvae.
• One arm of male removes a spermatophore from mantle cavity and inserts it into female.
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CheckYourUnderstanding
• Understandthetaxonomicrelationshipsandmajorfeaturesofmollusks
• Learntheexternalandinternalanatomyoftheclamandsquid
• Understandthemajoradvantagesandlimitationsoftheexoskeletonsofmollusksinrelationtothehydrostaticskeletonsofwormsandtheendoskeletonsofvertebrates,whichyouwillexaminelaterinthesemester